From an Italian perspective, what's odd in the American political system is that it's ... frozen. There are only two parties with realistic possibilities to get the power. And it's almost impossible that a new third party gains enough representatives to become significant. Even in UK this is not the rule [they have known, and they know, "coalition governments"]. I'm not going to talk about Italy: here we invent some new parties every year [!!]. This is a bit too much. But I'm wondering: can the US immobile two parties system a reason why the American political environment is so ... polarized and extreme? If the GOP or the Democrat Party needs even just 10 votes to win ... why not to involve also extremists [Fascists or Communists, to make it simple] in the life of the party? In a proportional system this risk doesn't exist. What do you think [from a perspective of political science] about this?